1. Field of Invention
This invention is directed to devices and methods for dissipating heat in fluid ejector heads.
2. Description of Related Art
A variety of devices and methods are conventionally used to dissipate heat in a thermal fluid ejector head. The thermal fluid ejector heads of fluid ejection devices, such as, for example ink jet printers, generate significant amounts of residual heat as the fluid is ejected by heating the fluid to the point of vaporization. This residual heat will change the performance and ultimately the ejection quality if the heat remains within the fluid ejector head. The ejector performance is usually seen by a change in the drop size, firing frequency, or other ejection metrics. Such ejection metrics are required to stay within a controllable range to have acceptable ejection quality. During lengthy operation or heavy coverage ejection, the temperature of the fluid ejector head can exceed an allowable temperature limit. Once the temperature limit has been exceeded, a slow down or cool down period is required to maintain the ejection quality.
Many fluid ejection devices, such as, for example, printers, copiers and the like, improve throughput by improving thermal performance. One technique to improve fluid ejector head performance is to divert excess heat into the fluid being ejected. Once the fluid being ejected has exceeded a predetermined temperature, the hot fluid is ejected from the fluid ejector head. During lengthy operation or during heavy area coverage ejection, this technique is also susceptible to temperatures in the fluid ejector head exceeding the maximum allowable temperature.
Another technique is to use a heat sink to store or conduct heat away from the fluid ejector head. Typically, these heat sinks are made from copper, aluminum or other materials having high thermal conductivity to remove heat from the fluid ejector head.
When such materials are used, however, the heat sink adds additional weight, size, cost and energy usage to the fluid ejector head, especially for fluid ejector heads that are translated past the receiving medium. Additionally, many fluids, such as inks, use solvents and/or salts which are likely to corrode aluminum or copper.
The heat sinks are typically bonded to a substrate. The substrate materials are often made from a conductive metal, such as aluminum or copper, that conducts heat away from a die module of the fluid ejector head. However, some fluid ejection devices use a plastic substrate that has a relatively low thermal conductivity. When metal heat sinks are used, the bond between the substrate and the die is subjected to significant stress due to temperature changes. The stress is generated from the large mismatch between the coefficients of thermal expansions of the substrate and the die.
These stresses create delaminating problems, where the die separates from the substrate, or the layers of the die separate. Also, the stress presents additional fluid ejection quality and reliability issues.